1. Field of the Invention
The present invention relates to a gas introducing and stirring apparatus for a metallurgical vessel such as an electric arc furnace or a basic oxygen furnace in a metallurgical field.
2. Description of Related Art
Recently, in a basic oxygen furnace and an electric arc furnace used in the steelmaking process, a few gas introducing nozzles of a refining gas are disposed on the furnace bottom, and through which oxygen, CO, CO.sub.2, hydrocarbon or inert gas is introduced to forcibly stir a molten metal, thereby enhancing the refining efficiency. Particularly, it is widely used universally in the electric arc furnace, in which an electric arc is used to melt steel scraps as a main raw material.
As means for introducing the refining gas from the furnace bottom, the following two means may be given. One is as shown in FIG. 6 and the other is as shown in FIG. 7.
FIG. 6, developed by the applicant, introduces the refining gas directly into the molten metal through each gas introducing nozzle 1 which consists of MgO-C material and in which small diameter pipes of stainless steel are buried, as shown in FIG. 6. In this type of gas introducing means, though the molten metal is stirred by convection, as shown in the figure, to enhance the stirring effect, when the refining gas is blown, the gas introducing nozzle 1 and its peripheral refractories are exposed to wear and tear by the molten metal and slag which are stirred forcibly as the refining proceeds.
Accordingly, the life of the gas introducing nozzle 1 is generally 150 to 350 heating, so that at the end of its service life the electric arc furnace 2 must be cooled down to replace or repair the gas introducing nozzle 1 and its peripheral refractories. As a result, the electric arc furnace must be shut off for five hours or more at a minimum including the cooling time of the furnace body, and the production ability of the electric arc furnace must be suspended.
Meanwhile, the latter means for introducing refining gas from the furnace bottom is disclosed in German Patent No. DE-3742861 and representatively shown in FIG. 7. A gas introducing nozzle 3 is buried in the refractory bricks of the furnace bottom 5 of the electric arc furnace 4, and the refining gas is introduced through pores of a ramming mass 6 having a low gas permeability different from a conventional higher density ramming mass of the furnace bottom 5. In the latter case, since the gas introducing nozzle 3 is not in direct contact with the molten metal, a life expectancy of the nozzle is the same as that of the ramming mass 6 of the furnace bottom 5 having the low gas permeability. Thus the nozzle is durable for more than a half year (3,000 heats) if only the ramming mass 6 and its upper wear lining material 7 are subjected to a hot repair.
In the case aforementioned, however, the refining gas is dispersed by a deflector plate 8 and introduced into a large area through the irregular plate of the ramming mass having lower gas permeability and lined throughout the furnace hearth, so that the position through which the refining gas is introduced into the molten metal are unstable, and the molten metal may not be stirred by convection as shown in the figure since the refining gas is dispersed widely, thus the metallurgical effect obtained by introducing the refining gas for stirring the molten metal is considerably deteriorated.
Furthermore, in this process, since the ramming mass of low gas permeability is used throughout the furnace hearth, lead is likely to permeate and accumulate in the ramming mass during use. Therefore, during a long time use, the pores in the ramming mass are clogged to block the refining gas. Besides, when the pores are clogged, the ramming mass of low gas permeability used throughout the furnace hearth must be replaced, resulting in an economical problem.
Accordingly, we have conducted various research such as burying an apparatus or apparatuses for introducing and stirring gas into the furnace bottom and surrounding its periphery by metal materials in an electric are furnace (Japanese Patent Application No. Hei 2-304584 (1990).